Valentin A. Chebanov

Aminoazoles as Key Reagents in Multicomponent Heterocyclizations

Because of the significant role in biological processes in living cells and the diverse types of physiological activities, heterocyclic compounds are in focus of intense investigations by academic and applied-oriented chemists. Considerably, a scientific renaissance of heterocycles during the last decades is closely related to the development of multicomponent approaches to their synthesis. Multicomponent methodology fundamentally different from two-component or sequential processes together with other innovative synthetic methods like microwave- and ultrasonic- assisted reactions offer some new possibilities in constructing heterocyclic systems with high level of molecular diversity and complexity. An overview of known multicomponent heterocyclizations using aminoazoles as a key reagent and their rich synthetic potential for obtaining five-, six-, and seven-membered heterocycles is presented. A special attention is paid to the tuning of chemo- and regio- and positional selectivity of some reactions as well as to the application of nonclassical activation methods based on microwave and ultrasonic irradiation.

Multicomponent heterocyclization reactions with controlled selectivity (Review)

The review is devoted to the problem of controlling the selectivity of multicomponent heterocyclizations. Special attention has been paid to analysis of the literature of the last decade concerning the use of nonclassical methods of activating chemical processes, such as microwave and ultrasonic irradiation.

Dotting the i's in three-component Biginelli-like condensations using 3-amino-1,2,4-triazole as a 1,3-binucleophile

Alternative reaction pathways for Biginelli-like cyclocondensation reactions using 3-amino-1,2,4-triazole as a 1,3-binucleophile under different reaction conditions lead to several types of products. The literary data is generalized and discussed. Additional results going beyond the generalization are also revealed.

Application of stable fused dienolates for diversity oriented synthesis of 2,5-dioxo-5,6,7,8-tetrahydro-2H-chromene-3-carboxamides

A novel one-pot three-step method for the synthesis of 2,5-dioxo-5,6,7,8-tetrahydro-2H-chromene-3-carboxamide derivatives via hydrolysis of 4-cyanobuta-1,3-dienolate salts was developed. These chromenes contain a 2-pyrone scaffold which is present in many well-known natural and synthetic biologically active compounds. Employing our protocol, a 55 compounds library was quickly generated from 1,3-cyclohexanediones, dimethylformamide dimethylacetal, and various N-substituted cyanacetamides.

Study of Three-Component Reactions Between 5-Amino-3-Methylisoxazole, N-Arylamides of Acetoacetic Acid, and Aromatic Aldehydes

A three-component cyclocondensation between 5-amino-3-methylisoxazole, N-arylamides of aceto-acetic acid, and aromatic aldehydes was studied under the conditions of thermal activation and ultrasonication. Upon heating in n-butanol, depending on the substituent in aldehyde, the reaction produced either N,4-diaryl-3,6-dimethylisoxazolо[5,4-b]pyridine-5-carboxamides, or their 4,7-dihydro derivatives. Ultrasonication unexpectedly produced N1,N3,2-triaryl-4-hydroxy-4-methyl-6-oxocyclo-hexane-1,3-dicarboxamides.

A MODIFIED BIGINELLI REACTION TOWARD OXYGEN-BRIDGED TETRAHYDROPYRIMIDINES FUSED WITH SUBSTITUTED 1,2,4-TRIAZOLE RING

A microwave-assisted Biginelli-like three-component condensation using salicylic aldehyde derivatives, acetone, and 5-substituted 3-amino-1,2,4-triazoles instead of the urea component results in the formation of oxygen-bridged tetrahydrotriazolopyrimidine derivatives (11,12-dihydro-5,11-methano[1,2,4]triazolo[1,5-c][1,3,5]benzoxadiazocines) in good yields and high purity. A plausible reaction mechanism for this transformation is discussed in details using literature and experimental data.

Reactions of 3(5)-Aminoisoxazoles Using Classical Methods of Activation, Microwave Irradiation, and Ultrasonication

This review offers an overview of data published over the previous four decades on the transformations of 3(5)-aminoisoxazoles in linear and multicomponent reactions. Particular attention has been focused on directed heterocyclizations using non-classical methods of activation – microwave irradiation and ultrasonication.

Intensification of ion exchange desorption of thiamine diphosphate by low-powered ultrasound

The process of ultrasound-assisted ion-exchange desorption of cocarboxylase (thiamine diphosphate (TDP)) from a strong acidic cation resin was studied. Kinetics studies revealed that ultrasound accelerates TDP desorption by 3 times. The optimal desorption parameters, viz. US power input, sonication time, eluent/resin ratio and the eluent (ammonium acetate buffer) concentration were established which were 15mW/cm3, 20min, 1:1 and 1M, respectively. The resin stability studies showed that the optimal ultrasonic power was less by the order than the resin degradation threshold which ensures durable and efficient resin exploitation during production. The resin sorption capacity remained unchanged even after 20 cycles of TDP sorption, ultrasonic desorption and resin regeneration. The recovery ratio of TDP was shown to increase non-linearly with decreasing the resin saturation factor, which can be attributed to diffusion limitations occurring during desorption. The optimal resin loading corresponding to more than 90 per cent of TDP recovery was found to be at the level of 10 per cent of the maximal sorption capacity. The study revealed 4-5-fold increase in concentrations of the recovered solutions, which together with process times shortening should result in considerable energy saving in downstream operations on production scale.

Heterocyclization Reactions of 3-methylisoxazol-5-amine with Pyruvic Acid Derivatives Using Classical and Non-classical Methods of Activation

Two- and multicomponent interactions between 3-methylisoxazol-5-amine and pyruvic acid derivatives were studied both by using classical methods of activation, as well as under microwave irradiation and ultrasonication. It was shown that the reactions with esters of arylidene pyruvic acids could lead to the formation of three different types of heterocyclic systems, while in the case of arylidene pyruvic acid a very insignificant conversion of the starting compounds to isoxazolo[5,4-b]pyridine carboxylic acids was observed, due to the low stability of 3-methylisoxazol-5-amine.

PHYSICAL AND CHEMICAL FACTORS IN MICROWAVE-ACCELERATED DRYING OF TEMPERATURE-SENSITIVE ORGANIC COMPOUNDS

We have conducted a comparative study of thermal (convective) and microwave drying processes for a temperature-sensitive compound, the drug substance cocarboxylase hydrochloride. We have shown that in a microwave field, we observe significant intensification of the drying process in all stages. We have analyzed the reasons for such intensification and we have determined the physical and chemical factors responsible for microwave-accelerated drying of temperature-sensitive organic compounds.